Bee Lian's Rich Orange Cake

Preheat oven to 350 degrees F (175 degrees C).Grease one 8 inch round cake pan. Sift flour and set aside.
Cream butter, sugar and grated orange zest until light and fluffy. Beat in the egg yolks one at a time. Fold in sifted flour, alternating with orange juice.
In another bowl, whisk egg whites until stiff and add a pinch of salt. Fold whisked egg whites into the mixture. Spoon batter into prepared pan.
Bake in preheated oven for 35 to 40 minutes, or until a toothpick inserted into cake comes out clean.